The present invention relates to ultraviolet radiation absorbing contact lenses and to a method for their preparation. More particularly, the invention relates to hydrophilic or "soft" contact lenses having a reactive ultraviolet radiation absorbing agent covalently bonded to polymeric material.
Ultraviolet radiation is ever present in our environment, and consists of wave lengths between 200-380 nm. Exposure to ultraviolet radiation has been found to be the cause of several ocular pathologies. The damaging effect of ultraviolet radiation on the corneal epithelium has been known for a long time. For instance, studies have demonstrated the damaging effect of 290 nm radiation on the rabbit corneal epithelium (Cullen, A. P. (1980): Ultraviolet Induced Lysosome Activity in Corneal Epithelium, Graefes Arch Clin Exp. Ophthalmol 214:107-118), as well as changes in the stroma and endothelium of primary corneal layers (epithelium, stroma and endothelium) subsequent to exposure to a commercially available UV suntan lamp which emits radiation across the full spectrum from 280 nm (Ringvold, A., et al. (1985): Changes in the Rabbit Corneal Stroma Caused by UV-Radiation, Acta Ophthalmol. (Copenh) 63:601-606). Compounding the damage is the fact that ultraviolet radiation damage to the eye is known to be cumulative and obeys the law of reciprocity. These findings reinforce the importance of adequate ocular protection against ultraviolet radiation. Such protection is particularly recommended for people who are prone to UV exposure, patients who have had cataract surgery and patients on photo-sensitizing drugs.
Recently, contact lenses have been developed which serve to absorb ultraviolet radiation. For example, U.S. Pat. No. 4,390,676 discloses an ultraviolet absorbing contact lens formed by copolymerizing a monomer suitable for making lenses and an ultraviolet absorber for absorbing radiation having wavelengths of 340 to 450 nm. The UV absorbing compound, 2-hydroxy-4-methacryloxy-benzophenone or mixtures thereof, is incorporated into the lens' polymeric material at the molecular level. Also, U.S. Pat. No. 4,528,311 discloses ultraviolet light absorbing contact lenses made of a polymeric composition comprising copolymers of 2-hydroxy-5-acrylyloxyphenyl-2H-benzotriazole with one or more other monomers copolymerizable therewith.
The above compounds have been found to copolymerize and give protection to the material. However, the copolymerization efficiency of the compounds has proved to be inadequate. Typically, no more than 15% of the alkenyloxy-benzophenones actually become part of the polymeric chain. The remainder of the material is easily leached out by solvent extraction. Furthermore, while the hydroxy benzophenones copolymerizable with acrylate monomers are effective UV absorbers and form chemically stable copolymers, relatively large amounts, i.e. 3 to 10% by weight, must be incorporated in the polymer to obtain 85% UV absorption at 400 nm and 1 mm thickness. Also, the compounds exhibit very broad absorption bands which extend into the visible spectrum, and lenses incorporating these ingredients tend to be unacceptably yellow in color.
The above described UV absorbing lenses also possess several limitations. For instance, the absorbing agents and the lens material have different properties, and only one absorbing agent is used and appears symmetrically as a thick film on the lens. As a result, the lenses have structural weaknesses and exhibit inconsistent expansion, which in turn results in overly curved or otherwise misshapened lenses. Furthermore, the application of the agent to the lens takes a relatively long time, must be done at high temperature, and requires a high concentration of the expensive agent.
There exists, therefore, a need for improved ultraviolet radiation absorbing contact lenses, as well as a method for their production.
There also exists a need for such lenses which have structural integrity, which can be prepared in relatively short time and at relatively low temperatures and which use small amounts of UV absorbing agents.
There exists a further need for such lenses which absorb a broad range of UV wavelengths.
There exists a more particular need for a lens which incorporates a relatively small amount of absorbing agent, which exhibits relatively little yellowing, and from which the absorbing agent does not leach out.